ok, so for those that havent read IA vol 9 yet, there's a new mission type called Boarding action/ Blood in the Void. if you have army builder and updated to ver 1.20, you'll have the option of making a list for it in there. they just goofed on changing their min troop choice code different for the new FOC. There's 2 sides, and both get their own FOC.

Attackers need 1-2 HQ, 1-4 Elites, 0-5 Troops, 0-2 Fast, 0-2 Heavy.

Defenders need 1-2 HQ, 0-4 Elites, 1-5 Troops, 0-1 Fast, 0-3 Heavy.

"Forces selected for fighting in a boarding action should be chosen from their codex as normal with the following exceptions:"No dedicated transport options.Vehicles except walkers and artillery mounted on no larger than a 60mm base are not allowed.In a codex space marine army, assault squads without jump packs count as Troops Choices.So with that, here's my list:

I don't really understand how a devastator squad would be useful in a boarding action. Wait, are you attacking or defending? I guess if you're defending it makes a bit more sense, but is still crazy expensive. I get the terminators, those are solid. How many points is that vanguard veteran squad? 260? For 5 guys in power armour? Wowzers. I'll take another 6 terminators instead please.

well for one, the devs are only 170. and remember that the rules will randomly make its all weapons str and higher rend. and anything with a blast template will send you flying into space, and causes pinning if it didnt already. also, the list is meant to play either attack or defend so im not carrying 2 lists in case i roll defender instead of attacker. thirdly, the vanguard are tooled as they are because they will be with a master apothecary who gives them feel no pain. FNP + plasma = win. also, including the apothecary, thats 6 plasma shots, and 18 power weapon attacks per turn. you wont be wanting to come against them in melee. also, one of my boarding action strategems is to give them void hardened armor, so they wont be affected by rending. so really, spending 265pts on 5 vanguard who attack at Init 4, and can run, and chase your retreating units and consolidate, is wirth it over another 5 termies who cant run or consolidate, etc. its like honour guard without taking a chapter master

Your unit will lose versus a dreadnought, a hive tyrant, or even 30 orks, and these are all far less in cost. These are things you will commonly see in boarding actions. The terminators have the utility to fight all of the above. I won't even mention how these units would fare head-to-head.

Obviously we have very different army building philosophies. You seem to favour small, elite units and I don't. That's cool. I know you have had a lot of success with your list so we can agree to disagree on the Vanguard and the value of 15 point plasma pistols

this is true, but i also dont own the models to field 10 man terminators. so that option is impossible. besides, this list is for the badab campaign we're starting and everyone playing is bringing space marines and so far, my opponents arent one to normally field dreads.